Your chick is too young to sex at this time, particularly since Brahmas are a slower maturing breed anyway. I would suggest re-posting its pic in a couple months. By then its gender should be pretty obvious.

Dark Brahmas are easier to sex than lights or buffs because the male and female feathering is so different. Brahmas can be slow to mature, but the feathering will be different early on for Darks. Females have lacing and penciling pattern all over. Males have solid or mostly black chests and white shoulders.